title: Predictability of excimer laser treatment of myopia and astigmatism by the VISX Twenty-Twenty. Melbourne Excimer Laser Group.
abstract: BACKGROUND
  To determine the predictability of excimer laser photorefractive keratectomy (PRK) to correct myopia, astigmatism, or both between -1.00 and -19.00 diopters (D).
  
  
  METHODS
  Royal Victorian Eye and Ear Hospital, East Melbourne, Australia.
  
  
  METHODS
  This study comprised 1218 consecutive eyes treated with a VISX Twenty-Twenty excimer laser and followed prospectively for 12 months. Low myopia was treated with one ablation zone (6.0 mm), high myopia with two ablation zones (5.0 and 6.0 mm), and extreme myopia with three ablation zones (4.5, 5.0, and 6.0 mm). Maximum spherical treatment was 15.00 D at the corneal plane. Data were analyzed to determine the predictability of the postoperative outcomes by preoperative refraction.
  
  
  RESULTS
  Nine hundred eighty eyes (80.5%) were available for the 12 month follow-up. The predictability of refraction and uncorrected and best corrected visual acuities progressively decreased with increasing myopia, although a comparable percentage of spherical correction was achieved at each diopter of myopia. The likelihood of losing lines of best corrected visual acuity and corneal haze increased with increasing myopia.
  
  
  CONCLUSIONS
  These data can be used to counsel patients of likely outcomes of excimer laser PRK to correct myopia.
authors.affiliation: Department of Opthalmology, University of Melbourne, Victoria, Australia.
authors.forename: H
authors.initials: H
authors.lastname: Higa
authors.forename: M
authors.initials: M
authors.lastname: Liew
authors.forename: C
authors.initials: C
authors.lastname: McCarty
authors.forename: H
authors.initials: H
authors.lastname: Taylor
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000503:physiopathology / Q000601:surgery*; D003315:Cornea / Q000503:physiopathology / Q000601:surgery*; D005500:Follow-Up Studies; D006801:Humans; D054018:Lasers, Excimer; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D018903:Photorefractive Keratectomy / Q000379:methods*; D011446:Prospective Studies; D012029:Refraction, Ocular; D015203:Reproducibility of Results; D016896:Treatment Outcome; D014792:Visual Acuity / Q000502:physiology